1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to conductor assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to shunt assemblies for circuit breaker conductor assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions.
The electrical contact assemblies of low-voltage circuit breakers, for example, generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The movable contact assembly includes a plurality of movable contact arms or fingers, each carrying one of the movable contacts and being pivotably coupled to a contact arm carrier. The contact arm carrier is itself pivotable about a number of pivot pins, pivoted by a protrusion or arm on the pole shaft of the circuit breaker operating mechanism to move the movable contacts into and out of electrical contact with the corresponding stationary contacts of the stationary contact assembly. The contact arm carrier includes a contact spring assembly structured to bias the fingers of the movable contact assembly against the stationary contacts of the stationary contact assembly in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear.
“Blow-on” schemes are commonly employed by low-voltage circuit breakers and are discussed, for example, in U.S. Pat. No. 6,005,206, which is hereby incorporated herein by reference.
The movable contact assembly is electrically connected to a generally rigid conductor of the conductor assembly by flexible conductors, commonly referred to as shunts. More specifically, each shunt is coupled at one end to the generally rigid conductor, and at the other end to a corresponding one of the fingers of the movable contact assembly. The shunts include a number of bends to accommodate the motion of the contact arm carrier and fingers with respect to the generally rigid conductor during a trip condition. Specifically, under over-current or fault conditions, energy flowing through the shunts results in a magnetic repulsion force which tends to straighten the bends of the shunts. However, the magnetic repulsion force is, in general, not translated into torque of the fingers of the movable contact assembly as efficiently and effectively as possible, resulting in blow-on performance of the circuit breaker that is less than desired. In other words, it is desirable to transfer the magnetic repulsion force associated with the shunts into positive torque (e.g., rotation) of the fingers in order to load the electrical contacts and thereby withstand relatively high fault currents.
There is, therefore, room for improvement in shunt assemblies for low-voltage circuit breaker conductor assemblies.